Surface acoustic wave (SAW) devices are often used in filtering applications for high-frequency signals. Of particular benefit is the ability to create low loss high order bandpass and notch filters without employing complex electrical filter circuits, which may require numerous active and passive components.
A common filtering application is in the transceiver circuitry of wireless communication devices. Often, an output of a first device is connected to an input of a SAW filter for filtering. The output of the SAW filter is generally associated with an output impedance, which is often different than the input impedance of a subsequent amplifier stage. As such, additional matching circuitry is used to provide an impedance transformation between the output of the SAW filter circuit and the input of the subsequent amplifier section. The inductive and capacitive elements used to form the matching network add significant cost to the design, and perhaps more importantly, take up space on the printed circuit board or module in which the circuit must be created. In mobile communications, there is always a need to decrease costs and minimize size. As such, there is a need for a more efficient technique to implement impedance matching in transceiver architectures.
Although SAW architectures have been used to provide minimalistic impedance transformations, the extent of the impedance transformation has traditionally been limited due to performance degradation. As the extent of the impedance transformation increases, the SAW architecture will inject significant losses into the signal being filtered. Further, the passband of the resultant filter may take on unfavorable characteristics, such as bandwidth narrowing or degradation in passband shape.
As such, there is a further need to provide a SAW architecture that is capable of supporting greater impedance transformations while minimizing losses to the signal being filtered and the injection of unwanted characteristics in the passband.